The present disclosure relates to a helical conveyor centrifuge.
Such a centrifuge can be configured as a solid-bowl helical conveyor centrifuge or as a sieve-bowl helical conveyor centrifuge.
DE 94 09 109 U1 discloses a centrifuge having an infinitely variable control of the differential speed between drum and broach.
WO 94/23223 shows a planetary gearing which is used to drive helical conveyor centrifuges.
From the magazine “Antriebstechnik 37 (1998, p. 39), a multistage differential gear drive is known. The gear drive has established itself as a gearing for driving decanters, since it allows a relatively good adjustment of differential speeds. As the preliminary stage it has a two-stage planetary gearing arrangement, which is configured as a four-shaft gearing, one shaft being secured during operation. The problem here is that, in order to cover a greater range of adjustable differential speeds, it is necessary to use a variety of variable speed and secondary motors or a variety of gear ratios. That makes standardization more difficult and, during operation, if a substantial change is made to the set differential speed, that may possibly necessitate a change of secondary motor.
According to DE 28 11 887 C3, two structurally mutually separate gearings are used as the gearing arrangement, which is relatively complex.
As part of the technological background, DE 198 06 374 C1, U.S. Pat. Nos. 3,343,786, 2,867,378 and WO 02/081094 are also cited.
EP 0 798 046 A1 discloses a centrifuge drive having two motors, a main motor and a variable speed motor, and a three-stage gearing. The first two gear stages are configured as epicyclic gear stages. At three shafts, a torque is either introduced into the gearing or is taken off therefrom. The output of the variable speed motor flows first into the first gear stage, from there into the second gear stage and from there to the downstream gear stage, so that the variable speed motor is necessarily designed for relatively large outputs. The gearing additionally poses the problem, in that it is relatively difficult to set small differential speeds in a precise manner.
The present disclosure is different in that it provides for a helical conveyor centrifuge in which a relatively large differential speed can be set without an exchange of a secondary motor. The present disclosure reveals that it is possible to set even small differential speeds in a relatively simple and precise manner.
The present disclosure relates to a helical conveyor centrifuge, such as a solid-bowl or sieve-bowl centrifuge. The centrifuge includes a rotatable drum, a rotatable screw disposed within the drum and a centrifuge drive for rotating the drum and the screw. The centrifuge drive is configured to set a differential speed between drum and screw. The centrifuge drive includes a first motor, a second motor, and a gearing arrangement disposed between the motors and also between the drum and the screw. The gearing arrangement includes a gearing arranged downstream of the motors, the gearing arrangement having a first gear, a second gear and a third gear stage. The first and second gear stages include at least four shafts, and torques are one of introduced into and taken off from the first and second gear stages. The first and second gear stages are disposed in a housing and are driven by at least three of the at least four shafts. The first motor feeds one of the torques into the housing via two of the at least four shafts, and the first motor feeds the torque into the first gear stage.
According to the present disclosure, at a total of at least four shafts, torques can be introduced into the first gear stage and the second gear stage or can be taken off from these two gear stages. The first and second gear stages are drivable, and generally also driven, at or by a total of at least three shafts, in which case the first motor firstly feeds a torque into the housing and secondly, at two shafts, feeds a torque into the first gear stage.
It is advantageous that the second motor for driving the second gear stage of the first gearing can remain the same for different differential speed ranges.
Moreover, the drawback, known from the prior art, that belt slippage, in the case of relatively small differential speeds, leads to unpredictable results, is avoided. Instead, the present disclosure allows a relatively precise setting of small differential speeds between drum and screw.
Moreover, the design according to the present disclosure is of simple and compact construction.
A presetting of the differential speed range can be realized in a simple manner by exchanging the belt drive for the first gear stage.
The accurate setting within the respective region is then effected by regulating or controlling the motor speed of the second motor.
The measure that the first gear stage is driven via three drive shafts, for example, via belt drives or directly and with two or three motors, means that no epicyclic power is generated and the number of belts can hence be kept low, so that the load upon the shafts in this region is low.
According to the present disclosure, a first motor is used as the main motor to drive the housing, so that an epicyclic gearing is realized. The main motor also drives the first gear stage doubly. Whereas, via a second motor, configured as a variable speed motor, a torque is introduced into the second gear stage, so that the screw is driven by the variable speed motor and by the main motor, whereas only the main motor rotates the drum.
It is expedient to split the power necessary for the screw drive between the secondary motor and the drum motor.
The variable speed motor then projects its speed range onto a small differential speed range.
The desired differential speed can hence be set with high accuracy. In terms of power, the variable speed motor and the associated frequency converter can be accurately designed for the range of adjustment which is necessary from a process engineering perspective and are thus not dimensioned unnecessarily large. The remaining power is supplied by the drum motor. In an embodiment of the present disclosure, this leads to better overall efficiency.
This splitting of the power between the two motors is managed in accordance with the movable differential speed ranges by varying the belt transmission ratio with the exchangeable pulleys.
Other aspects of the present disclosure will become apparent from the following descriptions when considered in conjunction with the accompanying drawings.